1. Field of the Invention
The present invention relates to an electronic still camera operable with a storage medium, e.g., a memory card removably mounted thereto and loaded with a semiconductor memory for storing image signals. More particularly, the present invention is concerned with an electronic still camera adaptive to storage media different in, for example, the storing speed of a semiconductor memory flexibly.
2. Description of the Related Art
A still camera has traditionally referred to an apparatus which stores images in a recording medium implemented as a film carrying a silver halide sensitive layer thereon. A recent achievement in the imaging art is an electronic still camera operable with a storage medium in the form of a semiconductor memory card and capable of storing images picked up in the medium in a digital signal format. A memory card applicable to this kind of camera accommodates a semiconductor memory therein as a memory device. While various memory devices different in type and operation characteristic are available today, an EEPROM ( Electrically Erasable Programmable Read Only Memory) is often used since it can store data without resorting to a battery. EEPROMs are generally classified into two types, i.e., a type capable of rewriting data on a byte basis and a type capable flushing away data. The byte-by-byte type EEPROM is not feasible for a memory card having a great capacity since reducing the cell size thereof is difficult, although data can be rewritten on a byte basis. The flush type EEPROM is provided with a collective erasure capability or a partial erasure capability, as needed. In any case, this type of EEPROM implements a memory card having a great capacity since the cells thereof can be made small size. Therefore, for an electronic still camera handling image data which is inherently great in amount, a memory card whose area for storing image data is implemented by a flush type EEPROM is advantageously usable.
However, the memory card using a flush type EEPROM, or flush memory card as referred to hereinafter, has some issues yet to be solved, as follows. The storing speed available with the flush memory card is low, compared to an SRAM (Static Random Access Memory). Further, the service life of this kind of memory card is short, regarding the number of times that data can be written in. Considering such specifications of parts lacking in unity, Japanese Electronic Industry Development Association (JEIDA) is endeavoring to standardize memory cards for use with an electronic still camera. Taking the contents of IC (Integrated Circuit) memory cards for personal computers as a reference for standard specifications, a speed version including operation speeds of 250 nanoseconds (ns), 200 ns, 150 ns, and 100 ns is defined.
Specifically, in a conventional electronic still camera, a memory card of the type described is connected to the camera via a connector built in the camera. As the camera picks up a desired scene, an optical image representative of the scene is focused onto a solid state image sensor by a lens. In response, the image sensor converts the optical image to a corresponding electric signal or image signal. An analog-to-digital converter transforms the image signal to a digital signal, or image data, and delivers it to a signal processing section. The image data undergone image processing, compression and other various kinds of signal processing at this section are transferred to the memory card and written thereto under the control of a controller.
The conventional electronic still camera, however, gives no consideration to the storing speed which differs from one memory card to another memory card. Specifically, a storing speed particular to a memory card is permanently assigned to each camera. For example, even when use is made of a memory card featuring a high storing speed, the camera simply writes image data in the card at the speed assigned thereto. Of course, a memory card whose storing speed is lower than that of the camera cannot be used.
In a continuous shoot mode operation, the speed available for writing data in a memory card determines the interval between continuous shots. This brings about a problem that when the shooting speed representative of the interval between shots is matched to a memory card whose storing speed is low, high-speed continuous shooting cannot be effected. An electronic still camera is a promising implementation for high-speed continuous shooting since it does not need, for example, the traditional mechanism for rolling up a film. However, the problem stated above prevents the camera from exhibiting such a capability sufficiently. Although a memory card having a high storing speed may be mounted to the camera, the characteristic or the effect particular to the card is not available since the continuous shooting speed of the camera itself is not variable.